Tire

ABSTRACT

A tire which has a bead filler ( 5 ) arranged on the outside in the tire radius direction of one pair of bead sections provided at the right and left thereof, one pair of side wall sections ( 6 ) provided in the right and left of a tread section, and a rubber reinforcing layer ( 7 ) arranged in the side wall section ( 6 ), characterized in that the rubber composition constituting the bead filler ( 5 ) or the rubber reinforcing layer ( 7 ) comprises a conjugated diene based polymer having a vinyl bond content of 25% or more, a weight average molecular weight (Mw) of 200,000 to 900,000 and a molecular weight distribution (Mw/Mn) represented by the ratio of a weight average molecular weight (Mw) to a number average molecular weight (Mn) of 1 to 4 in an amount of 50 mass % or more of the rubber component thereof, and a resin and a curing agent therefor in a total amount of 3 parts by mass or more relative to 100 mass parts of the rubber, and exhibits a modulus of elasticity at 100% elongation at 25° C. of 5 MPa to 20 MPa and a dynamic modulus of elasticity at room temperature of 10.5 MPa or less.

BACKGROUND OF THE INVENTION

The present invention relates to a tire on which influence is notexerted by a puncture caused by an external injury, specifically to atire which is excellent in a durability (run flat durability) in runningafter the tire is injured and a vibration riding comfort (ridingcomfort) in usual running.

RELATED ART

In a tire, a side-reinforcing layer by a rubber composition or acombined material of a rubber composition with a fiber has so far beenprovided in order to elevate a rigidity of a side wall part. In the caseof running when an internal pressure of a tire is reduced by a puncture,a so-called run flat running state, a side-reinforcing layer isincreased in deformation in proportion with an increase in deformationof a side wall part in a tire, and heating goes on and reaches to 200°C. or higher in a certain case. In such state, the side-reinforcinglayer exceeds a fracture limit and leads to failure of the tire.

A means for extending time which passes until failure is caused includesan increase in a volume of rubber such as an increase in the maximumthicknesses of a side-reinforcing layer and a bead filler which areprovided. Assuming of such means results in bringing about anundesirable situation such as a deterioration in a riding comfort, anincrease in a weight and an increase in a noise level.

If a side-reinforcing layer and a bead filler which are provided aredecreased in a volume in order to avoid the situation described above,for example, a deterioration in a riding comfort, a load in run flat cannot be supported, and a side wall part of the tire is deformed in runflat to a very large extent to bring about an increase in heating of therubber composition. As a result thereof, there used to be the problemthat the tire leads to failure in an earlier stage.

In the case of reducing more an elasticity of rubber used by changing amaterial blended, a load in run flat can not be supported as well, and aside wall part of the tire is deformed to a very large extent to bringabout an increase in heating of the rubber composition. As a resultthereof, brought about is the existing situation that the tire leads tofailure in an earlier stage.

DISCLOSURE OF THE INVENTION

Under such circumstances, an object of the present invention is toprovide a tire in which a riding comfort of a run flat tire in normalrunning is maintained and improved and in which a run flat durability asa function of the run flat tire is extraordinarily elevated by scheminga rubber composition used for a bead filler and a side-reinforcinglayer.

Investigations repeated by the present inventors in order to achieve theobject described above have resulted in finding that a tire in which arubber composition having specific physical properties which comprises aspecific conjugate diene base polymer, a resin and a curing agent forthe resin is used for at least one of a bead filler and aside-reinforcing layer maintains and improves a riding quality of a runflat tire in normal running and that it extraordinarily raises a runflat durability which is a function of the run flat tire. The presentinvention has been completed based on the above knowing.

That is, the present invention provides a tire comprising a pair of leftand right bead parts, a bead filler and a carcass layer which areprovided at an outside part in a tire radius direction of the above beadpart, a tread part provided at an outside part in a tire radiusdirection of the above carcass layer, a pair of side wall parts providedat left and right sides of the above tread part and a rubber-reinforcinglayer provided at the above side wall part, wherein both of a rubbercomposition constituting the bead filler described above and/or a rubbercomposition constituting the rubber-reinforcing layer provided at theside wall part in a maximum thickness of 6 to 13 mm contain in a rubbercomponent, 50% by weight or more of a conjugate diene base polymer whichhas a vinyl bonding amount of 25% or more and a weight average molecularweight (Mw) of 200,000 to 900,000 and in which a ratio (Mw/Mn) of aweight average molecular weight (Mw) to a number average molecularweight (Mn) is 1 to 4; and the rubber composition contains a resin and acuring agent therefor in a total amount of 3 mass parts or more per 100mass parts of the rubber and has an elastic modulus of 5 to 20 MPa in100% elongation at 25° C. and a dynamic elastic modulus of 10.5 MPa orless at a room temperature.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partial cross-sectional drawing showing one example of thetire of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, a tire in which a rubber compositioncontaining 50% by weight or more of a conjugate diene base polymer inwhich a vinyl bonding amount in a diene unit of the conjugate diene basepolymer, a weight average molecular weight (Mw) and a molecular weightdistribution (Mw/Mn) are limited in the specific ranges described aboveand containing a resin and a curing agent therefor in a total amount of3 mass parts or more per 100 mass parts of the rubber is used for atleast one of a bead filler and a side-reinforcing layer is markedlyeffective for inhibiting a reduction in a dynamic elastic modulus (E′)caused by a rise in a temperature of the above-rubber composition and anincrease in a loss tangent (tan δ). Accordingly, a side wall part of thetire can be inhibited from increasing in deformation in run flatrunning, and the run flat durability can be raised.

In the present invention, the vinyl bonding amount in the conjugatediene unit described above has to be 25% or more based on the dienebonding part of the polymer described above. If the vinyl bonding amountis less than 25%, a reduction in the dynamic elastic modulus (E′) causedby breakage of sulfur cross-linking at a high temperature of 150° C. orhigher is dominant, and therefore an effect of inhibiting a reduction inthe elastic modulus caused by a rise in the temperature can not beexpected to be sufficiently exhibited. Further, an increase in the losstangent (tan δ) is caused in a certain case. From this point of view,the vinyl bonding amount is preferably 30% or more, more preferably 35%or more. It is particularly preferably 40 to 60%.

A weight average molecular weight (Mw) of the polymer described abovehas to be 200,000 to 900,000. If the above weight average molecularweight (Mw) is less than 200,000, the rubber composition tends to beinferior in a tensile characteristic and a rolling characteristic, andif it exceeds 900,000, the rubber composition tends to be inferior in aprocessability. From this point of view, the weight average molecularweight (Mw) is preferably 300,000 to 800,000.

Further, the molecular weight distribution (Mw/Mn) has to be 1 to 4. Ifit exceeds 4, the heating property tends to be lowered, and it tends tobe difficult to maintain the elastic modulus in a temperature area of150° C. or higher.

The conjugate diene base polymer in the present invention is preferablya conjugate diene homopolymer and/or a conjugate diene-aromatic vinylcopolymer, and it includes modified polymers thereof as described later.

In this respect, the conjugate diene monomer includes, for example,1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene, and among them,1,3-butadiene is preferred.

An aromatic vinyl monomer used for copolymerization with the conjugatediene monomer includes, for example, styrene, α-methylstyrene,1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene,4-cyclohexylstyrene and 2,2,6-tolylstyrene, and among them, styrene ispreferred.

The conjugate diene base polymer in the present invention is preferablya conjugate diene base polymer having a vinyl bonding amount of 25% ormore in the conjugate diene unit, a weight average molecular weight (Mw)of 200,000 to 900,000 and a molecular weight distribution (Mw/Mn) of 1to 9 which is represented by a ratio of a weight average molecularweight (Mw) to a number average molecular weight (Mn) and containing atin atom and/or a nitrogen atom in a molecule. In the present invention,the conjugate diene base polymer is preferably polybutadiene and astyrene-butadiene copolymer, and among them, polybutadiene is preferred.

The rubber composition in the present invention has to contain 50 mass %or more of the conjugate diene base polymer described above in therubber component. If it is less than 50 mass %, a reduction in theelastic modulus caused by a rise in the temperature can not be inhibitedin a certain case, and a reduction in the dynamic elastic modulus causedby a rise in the temperature and an increase in the loss tangent (tan δ)can not be inhibited in a certain case. From this point of view, 60 mass% or more of the polymer described above is preferably contained in therubber component.

The above composition containing the conjugate diene base polymerdescribed above is notably effective for inhibiting a reduction in theelastic modulus caused by a rise in the temperature and inhibitsdeformation of the side part caused by run flat running, and thereforethe run flat durability can be raised.

In the rubber composition used in the present invention, other rubbercomponents which can be mixed with the conjugate diene base polymerdescribed above shall not specifically be restricted, and they include,for example, natural rubber, polyisoprene synthetic rubber (IR),cis-1,4-polybutadiene rubber (BR), styrene-butadiene rubber (SBR),acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR) and butylrubber (IIR). The above rubbers may be used in combination of two ormore kinds thereof.

The rubber composition in the present invention has to contain a resinand a curing agent therefor in a total amount of 3 mass parts or moreper 100 mass parts of the rubber component described above. If theamount is less than 3 mass parts, the desired tensile elastic modulus isnot obtained, and if it is 10 mass parts or more, the rubber isincreased in a loss tangent (tan δ) and reduced in a run flat durabilityin a certain case.

Accordingly, the resin and the curing agent therefor described above arecontained preferably in a total amount of 3 mass parts or more and lessthan 10 mass parts. This makes it possible to allow the rubbercomposition of the present invention to be improved in a 100% tensileelastic modulus without sacrificing the other performances, for example,a dynamic elastic modulus.

In this case, an amount ratio of the phenol resin to the curing agentused for the rubber composition described above is 10/90 to 90/10,preferably 90/10 to 50/50.

A thermosetting resin such as a phenol base resin and a melamine resinis used as the resin. Among them, a phenol base resin is particularlypreferred.

The phenol base resin described above is oligomers and polymers obtainedby condensing phenols with aldehydes. Used as the phenols are phenol,lower alkylphenols such as respective cresols, xylenols andtert-butylphenol, higher alkylphenols such as nonylphenol, cashew oiland lignin and divalent phenols such as resorcin and catechol.Formaldehyde is mainly used for the aldehydes.

The principal phenol resin includes, phenol-formaldehyde resins,resorcin-formaldehyde resins and cresol resins, and thephenol-formaldehyde resins are particularly preferred.

In addition to 100% phenol resins, natural resin-modified phenol resinsand oil-modified phenol resins can be used for the phenol resin.

A novolak type resin which is a two step resin cured with a curing agentis preferably used for the phenol base resin.

The curing agent includes hexamethylenetetramine andhexamethoxymethylmelamine. The combination thereof can freely beselected, and a plurality of the resins and the curing agents may beselected respectively. Also, the resins containing the curing agent maybe used.

Further, in order to achieve the object of the present invention by therubber composition of the present invention, the elastic modulus in 100%elongation has to be 5 to 20 MPa at 25° C., and the dynamic elasticmodulus (E′) at a room temperature has to be 10.5 MPa or less.

The elastic modulus in 100% elongation has preferably a larger valuebecause of necessity to support the load in run flat running. Also, thedynamic elastic modulus (E′) at a room temperature has preferably asmaller value from the viewpoint of securing the riding comfort.

As the combination of the resin and the curing agent described aboveelevates the elastic modulus in 100% elongation but less elevates thedynamic elastic modulus (E′), less influence is exerted on the ridingcomfort, and the riding comfort can be controlled by varying an amountof a filler such as carbon black.

The rubber composition containing the conjugate diene base polymerdescribed above in the present invention can suitably contain, inaddition to the respective components described above, variouscompounding agents including a vulcanizing agent such as sulfur andperoxides, a vulcanization-accelerator, an antioxidant, a softeningagent, a reinforcing filler, an inorganic filler, a phenol resin an acuring agent. Further, the rubber composition of the present inventionmay be a combined matter with particles, fibers and cloths of variousmaterials.

The tire of the present invention can be produced by applying the rubbercomposition described above to at least one of the bead filler and theside-reinforcing layer provided at the side wall part by a conventionalmethod.

Air which is usual or changed in an oxygen partial pressure or inert gassuch as nitrogen can be used as gas charged into the tire.

Next, the tire of the present invention shall be explained according tothe drawing attached.

FIG. 1 is a cross-sectional drawing of a left half part in one exampleof the tire of the present invention, and the above tire 1 comprises apair of left and right ring-like bead cores 4, a bead filler 5 providedat an outside part in a tire radius direction of the above bead core 4,a carcass layer 2 comprising at least one ply in which plural paralleledcords are buried in a coating rubber, a belt layer 3 provided at anoutside part in a tire radius direction of the above carcass layer 2, atread part 8 provided in a tire radius direction of the above belt layer3, a pair of side wall parts 6 provided at left and right sides of theabove tread part 8 and a rubber-reinforcing layer 7 provided at theabove side wall part 6.

The carcass layer 2 has a folded carcass ply 2 a and a down carcass ply2 b, and both ends of the folded carcass ply 2 a are folded around thebead core 4 to form a folded end part. The bead filler 5 is situatedbetween the folded carcass ply 2 a and the folded end part thereof, andthe down carcass ply 2 b is situated-between the side wall part 6 andthe folded end part of the folded carcass ply 2 a.

The rubber-reinforcing layer 7 is provided on an inside peripheraldirection face in the side wall part 6 of the folded carcass ply 2 a.The rubber-reinforcing layer 7 reinforcing the side wall part 6 isprovided in a maximum rubber thickness of 6 to 13 mm. The rubber of therubber-reinforcing layer 7 may be a combined matter with organic fibersand inorganic particles, and the cross-sectional form thereof shall notspecifically be restricted as long as it has a function of reinforcingthe side.

In the tire of the present invention, at least one of the bead filler 5and the rubber-reinforcing layer 7 each described above is formed usingthe rubber composition described above to thereby make it possible tomaintain and improve a riding comfort of a run flat tire in normalrunning and extraordinarily elevate a run flat durability which is afunction of the run flat tire.

Next, the present invention shall be explained in further details withreference to examples, but the present invention shall by no means berestricted by these examples.

Various measured values were determined according to methods describedbelow.

Physical properties of conjugate diene base polymer high vinylpolybutadiene rubber:

(1) Microstructure of the Polymer

A vinyl bond (1,2-bond) in the conjugate diene unit was determined by aninfrared method (Morello method).

(2) Weight Average Molecular Weight (Mw) of the Polymer

The weight average molecular weight (Mw) of the polymer was measured bygel permeation chromatography [GPC: HLC-8020 manufactured by Toso Co.,Ltd., column: GMX-XL (2 column series) manufactured by Toso Co., Ltd.],and it was determined using a differential refractive index (RI) interms of polystyrene using monodispersed polystyrene as a standard.Performances of vulcanized rubber:

(1) Dynamic Storage Elastic Modulus (E′)

A sheet having a width of 5 mm and a length of 40 mm was cut out from aslab sheet having a thickness of 2 mm which was obtained by vulcanizingthe rubber composition on the conditions of 160° C. and 12 minutes toprepare a sample. A dynamic storage elastic modulus of the above samplewas measured by means of a spectrometer manufactured by Ueshima MFG Co.,Ltd. on the measuring conditions of a distance of 10 mm between chucks,an initial distortion of 200 micrometer (micron), a dynamic distortionof 1%, a frequency of 52 Hz, a measurement-commencing temperature of250° C., a temperature-elevating speed of 3° C./minute and ameasurement-finishing temperature of 250° C.

(2) Tensile Elastic Modulus

The tensile elastic modulus was measured according to JIS K6251.

Test of Experimental Tire:

(1) Run Flat Durability

The respective experimental tires were rim-assembled at an atmosphericpressure and charged with air at an internal pressure of 230 kPa, andthen a core of a valve was pulled out after left standing for 24 hoursin a room of 38° C. to turn an internal pressure to an atmosphericpressure. A drum running test was carried out on the conditions of aload of 4.17 kN (425 kg), a speed of 89 km/b and a room temperature of38° C. A distance running until a trouble was caused was defined as arun flat durability and shown by an index in the examples, wherein avalue of Comparative Example 1 was set to 100. The larger the index, thebetter the run flat durability.

(2) Riding Comfort

An experimental tire was installed in a passenger car to carry out afeeling test of a riding comfort by two professional drivers, and it wasevaluated by a score of 1 to 10 to determine an average value thereof.The larger the value, the better the riding comfort.

PRODUCTION EXAMPLE Conjugate Diene Base Polymer

A 15 mass % cyclohexane solution of dried butadiene was continuouslyintroduced into a pressure proof reaction apparatus of 8 liter equippedwith a temperature-controlling jacket which was substituted withnitrogen at a speed of 200 g/minute. Further, 15 mmol/minute of a 1mol/liter cyclohexane solution of ditetrahydrofurylpropane (DTHFP) and0.2 mmol/minute of a n-hexane solution of n-butyllithium werecontinuously introduced thereinto from the same port. The polymerizationsystem was always maintained at 80° C., and the resulting polymer wascontinuously taken out from an upper part of the reactor. It was throwninto 1 mass % isopropanol of 2,6-di-t-butyl-p-cresol (BHT) to obtain apolymer. No precipitation was observed in the polymer since commencingof the polymerization through the completion thereof, and it was evenlytransparent.

The polymerization conversion rate was almost 100%. Further, the solidmatter was dried to obtain a rubber-like polymer. This polybutadiene wasmeasured for a vinyl bonding amount, a weight average molecular weight(Mw) and a molecular weight distribution. It had a vinyl bonding amountof 50%, a weight average molecular weight (Mw) of 300,000 and amolecular weight distribution (Mw/Mn) of 2.1.

EXAMPLES 1 TO 3 AND COMPARATIVE EXAMPLES 1 TO 4

A rubber component 100 parts by weight having a kind and an amount eachshown in Table 1 was blended with carbon black, a resin and a curingagent, a process oil, zinc oxide, stearic acid, an antioxidant 6C, avulcanization-accelerator NS and sulfur to prepare a rubber composition.

The rubber composition described above was used for a side wallpart-reinforcing layer and a bead filler to produce a radial tire for apassenger car having a size of 215/45ZR17 by a conventional method. Thetire was evaluated for a riding comfort and a run flat durability. Amaximum thickness of the side wall part-reinforcing layer was describedin Table 1 as a reinforcing rubber gauge. The results thereof are shownin Table 1. TABLE 1 Example Comparative Example 1 2 3 1 2 3 4 Naturalrubber 30 30 30 30 30 30 30 BR^(*1) 70 70 70 High Vinyl BR^(*2) 70 70 7070 Carbon black^(*3) 30 40 50 40 40 40 30 Phenol resin^(*4) 3 3 3 3 3Curing agent 1 1 1 1 1 (hexamethylene- tetramine)^(*5) Curing agent 2 22 2 2 (hexamethoxy- methylmelamine)^(*6) Elastic modulus 6.2 7.3 9.6 5.34.8 7.3 6.1 in 100% elongation (MPa) Room temperature 1% 6.5 8.5 10.415.5 7.2 16.8 14.5 distortion dynamic elastic modulus (MPa) Run flatdurability 105 120 150 100 70 120 105 Riding comfort 7.0 6.5 5.5 5.0 7.04.5 5.0 Reinforcing 8.0 8.0 8.0 8.0 8.0 8.0 8.0 rubber gauge (mm)Remarks^(*1)Polybutadiene rubber: [BR01] (cis-1,4-polybutadiene, vinyl bondingamount 2.5%, manufactured by JSR Co., Ltd.)^(*2)Conjugate diene base polymer: (high vinyl polybutadiene: vinylbonding amount 50%, weight average molecular weight (Mw) 500,000,molecular weight distribution (Mw/Mn) 2.1)^(*3)Carbon black: GPF (brand name: Asahi #55, manufactured by AsahiCarbon Co., Ltd.)^(*4)Phenol resin: phenol.formaldehyde resin (novolak type, manufacturedby Sumitomo Bakelite Co., Ltd.)^(*5)Hexamethylenetetramine: manufactured by Ohuchishinko ChemicalIndustrial Co., Ltd.^(*6)Hexamethoxymethylmelamine: manufactured by Mitsui Cytec Co., Ltd.

As shown in Table 1, it can be found from comparison of, for example,Example 2 with Comparative Example 2 that the tire of the presentinvention in which a rubber composition having specific physicalproperty values blended with a conjugate diene base polymer havingspecific properties in the present invention and comprising a resin suchas a phenol resin and a curing agent is used for a side wallpart-reinforcing rubber for a tire and/or a bead filler rubber for atire maintains and improves a riding comfort of a run flat tire innormal running and extraordinarily elevates a run flat durability whichis a function of the run flat tire.

INDUSTRIAL APPLICABILITY

According to the present invention, applying of a rubber compositionhaving specific physical property values blended with a conjugate dienebase polymer having specific properties and comprising a resin such as aL phenol resin and a curing agent therefor to a rubber-reinforcing layerin a side wall part of a tire and/or a bead filler rubber makes itpossible to provide a tire in which a riding comfort of a run flat tirein normal running is maintained and improved and in which a run flatdurability as a function of the run flat tire is extraordinarilyelevated.

1. A tire comprising a pair of left and right bead parts, a bead fillerand a carcass layer which are provided at an outside part in a tireradius direction of the above bead part, a tread part provided at anoutside part in a tire radius direction of the above carcass layer, apair of side wall parts provided at left and right sides of the abovetread part and a rubber-reinforcing layer provided at the above sidewall part, wherein a rubber composition constituting the bead fillerdescribed above contains in a rubber component, 50 mass % or more of aconjugate diene base polymer which has a vinyl bonding amount of 25% ormore and a weight average molecular weight (Mw) of 200,000 to 900,000and in which a molecular weight distribution (Mw/Mn) shown by a ratio ofa weight average molecular weight (Mw) to a number average molecularweight (Mn) is 1 to 4; and the rubber composition contains a resin and acuring agent therefor in a total amount of 3 mass parts or more per 100mass parts of the rubber and has an elastic modulus of 5 to 20 MPa in100% elongation at 25° C. and a dynamic elastic modulus of 10.5 MPa orless at a room temperature.
 2. A tire comprising a pair of left andright bead parts, a bead filler and a carcass layer which are providedat an outside part in a tire radius direction of the above bead part, atread part provided at an outside part in a tire radius direction of theabove carcass layer, a pair of side wall parts provided at left andright sides of the above tread part and a rubber-reinforcing layerprovided at the above side wall part, wherein a rubber compositionconstituting the rubber-reinforcing layer provided at the side wall partdescribed above in a maximum thickness of 6 to 13 mm contains in arubber component, 50 mass % or more of a conjugate diene base polymerwhich has a vinyl bonding amount of 25% or more and a weight averagemolecular weight (Mw) of 200,000 to 900,000 and in which a molecularweight distribution (Mw/Mn) shown by a ratio of a weight averagemolecular weight (Mw) to a number average molecular weight (Mn) is 1 to4; and the rubber composition contains a resin and a curing agenttherefor in a total amount of 3 mass parts or more per 100 mass parts ofthe rubber and has an elastic modulus of 5 to 20 MPa in 100% elongationat 25° C. and a dynamic elastic modulus of 10.5 MPa or less at a roomtemperature.
 3. A tire comprising a pair of left and right bead parts, abead filler and a carcass layer which are provided at an outside part ina tire radius direction of the above bead part, a tread part provided atan outside part in a tire radius direction of the above carcass layer, apair of side wall parts provided at left and right sides of the abovetread part and a rubber-reinforcing layer provided at the above sidewall part, wherein both of a rubber composition constituting the beadfiller described above and a rubber composition constituting therubber-reinforcing layer provided at the side wall part described abovein a maximum thickness of 6 to 13 mm contain in a rubber component, 50mass % or more of a conjugate diene base polymer which has a vinylbonding amount of 25% or more and a weight average molecular weight (Mw)of 200,000 to 900,000 and in which a molecular weight distribution(Mw/Mn) shown by a ratio of a weight average molecular weight (Mw) to anumber average molecular weight (Mn) is 1 to 4; and the rubbercomposition contains a resin and a curing agent therefor in a totalamount of 3 mass parts or more per 100 mass parts of the-rubber and hasan elastic modulus of 5 to 20 MPa in 100% elongation at 25° C. and adynamic elastic modulus of 10.5 MPa or less at a room temperature. 4.The tire as described in claim 1, 2 or 3, wherein the resin describedabove is a phenol base resin.